Abstract
The transition of the freeze–thaw state of the land surface soil occurs every year with the season and is closely related to the human living environment. The freezing and thawing changes of the ground surface have important effects on hydrological activities, meteorological conditions, and ecological gas dynamics. Traditional monitoring methods have their limitations. In the past two decades, the emerging GNSS-R/IR (Global Navigation Satellite System-Reflectometry/Interference Reflectometry) technology has provided a new method for monitoring the surface f state; however, fewer works have paid attention to the scattering mechanism models in the current study. In this paper, a forward GNSS multipath model suitable for a complex cold surface is developed. The dielectric constant model with different surface parameters is added. The calculation of snow layer attenuation is employed to take the snow cover into consideration. Based on the first-order radiation transfer equation model, a polarization synthesis method is used to obtain the circularly and linearly polarized vegetation specular scattering characteristics. The surface characteristics and antenna model are coupled. A more detailed forward GNSS multipath model of frozen and thawed soil under complex surface conditions is established. The model is used to simulate and analyze the forward GNSS multipath (Signal to Noise Ratio (SNR), phase and pseudorange) responses of frozen and thawed soil under complex surface conditions (soil salinity, snow and vegetation coverage). Studies have shown that when the soil changes from freezing to thawing due to the change in the phase of the water in the soil, the dielectric constant and BRCS (bi-static radar cross-section) increase, causing the increase in the amplitude of the multipath observation. The higher the salinity content, the larger the amplitude of the multipath observation. The attenuation of the snow cover and the vegetation layer will lead to the reduction of the multipath observation amplitude. For the first time, the model developed by this paper reveals the GNSS multipath observation response of frozen and thawed soil under complex surface conditions in detail, which can provide some theoretical support for subsequent experimental design and data analysis.
Highlights
As one of the important components of the cryosphere, frozen soil refers to all kinds of rocks and soils that contain ice and unfrozen water at temperatures of zero degrees Celsius and below
We have developed a model that can be used to analyze the effects of soil salinity, vegetation and snow cover in frozen and thawed soil on GNSS multipath observations (SNR, phase and pseudorange)
This section simulates the relationship between the corresponding dielectric constant model, Bistatic Radar Cross-Section (BRCS) and GNSS multipath observations when the salinity in the soil solution changes
Summary
As one of the important components of the cryosphere, frozen soil refers to all kinds of rocks and soils that contain ice and unfrozen water at temperatures of zero degrees Celsius and below. The spatial resolution of this remote sensing method is about 1 km, which is between the traditional site sensor (100 km2) This means that thousands of GPS station data can be used for near-real-time observation of ground geophysical features, and they can provide data for. Larson et al [7] used the observation data of a station in Colorado to conduct research and analysis, and they pointed out that there was a linear correlation between the phase and the near-surface soil moisture [11]; Zavorotny et al [12] used the GPS reflection information model to indicate its physical mechanism. Chew et al used the GNSS-R mode of SMAP (Soil Moisture Active Passive) data (receiver frequency bandwidth adjustment, etc.) to conduct a preliminary analysis of surface freeze–thaw state monitoring [15].
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